An injection mould of this type is disclosed in PATENT ABSTRACTS OF JAPAN, Vol. 13, No. 41 (M-791) (3389), 30 Jan. 1989. In this known mould the mould sections which are moved relative to one another to break a sprue are driven apart by spring force. After these mould sections have moved a limited distance apart, the actual mould is opened to release the product. In order to ensure that the sprue of the product is broken before release starts and to guarantee the sequence of this movement, it is necessary to use relatively heavy springs to guarantee breakage of the sprue. Even if relatively heavy springs of this type are used it is still not always guaranteed that breakage takes place.
This relatively large spring force has to be overcome again when closing the mould before the start of a new injection cycle. This implies that any safety measures fitted which serve to stop the closing movement of the mould if undesired articles are present between the mould sections, or in the case of other irregularities, must have a minimum response force which is equal to the spring pressure to be overcome.
In practice this means that moulds of this type can not be provided with a blocking protection which functions realistically. Consequently it is necessary to fit complex cover constructions around the mould, the movement of the various sections of the mould being interrupted as soon as such a cover is opened. This is a circuitous and undesirable construction with which, moreover, it is not possible to prevent damage occurring to the product and/or mould during the closing movement if, for example, injection moulding residues are in the wrong place. The use of a cover is merely a safety precaution for operators and does not protect the mould and/or the products to be injected. The aim of the invention is to overcome these disadvantages.